The present invention relates to an electrophotographic recording material comprising an electrically conductive support and at least one photoconductive layer which comprises an organic photoconductor, a sensitizing dye, a binder, and customary additives.
German Pat. No. 1,058,836 corresponding to U.S. Pat. No. 3,189,447) discloses the use of organic photoconductors in an electrophotographic reproduction process. These organic photoconductors generally have a spectral sensitivity in the long-wave ultraviolet spectral region from about 350 to 450 nm.
In order to extend the range of spectral sensitivity to about 650 nm, it is known to use sensitizers comprising a wide variety of dyes of different chemical types. A list of dyes which are effective for this purpose appears, for example, in Schultz' Dye Tables (7th edition, volume 1, 1931), which includes:
Triarylmethane dyes, for example, PA0 xanthene dyes, i.e., rhodamines, for example, PA0 and phthaleins, for example, PA0 thiazine dyes, for example PA0 acridine dyes, for example, PA0 quinoline dyes, for example, PA0 quinone dyes and ketone dyes, for example,
Brilliant Green (No. 760, page 314), PA1 Victoria Blue B (No. 822, page 347), PA1 Methyl Violet (No. 783, page 327), PA1 Crystal Violet (No. 785, page 329), and PA1 Acid Violet 6B (No. 831, page 351); PA1 Rhodamine B (No. 864, page 365), PA1 Rhodamine 6G (No. 866, page 366), PA1 Rhodamine G Extra (No. 865, page 366), PA1 Sulforhodamine B (No. 863, page 364), and PA1 Fast Acid Eosin G (No. 870, page 368), PA1 Eosin S (No. 883, page 375), PA1 Eosin A (No. 881, page 374), PA1 Erythrosin (No. 886, page 376), PA1 Phloxin (No. 890, page 378), PA1 Bengal Rose (No. 889, page 378), and PA1 Fluorescein (No. 880, page 373); PA1 Methylene Blue (No. 1038, page 449); PA1 Acridine Yellow (No. 901, page 383), PA1 Acridine Orange (No. 908, page 387), and PA1 Trypaflavin (No. 906, page 386); PA1 Pinacyanol (No. 924, page 396), and PA1 Cryptocyanine (No. 927, page 397); PA1 Alizarin (No. 1141, page 449), PA1 Alizarin Red S (No. 1145, page 502), and PA1 Quinizarin (No. 1148, page 504); and cyanine dyes. PA1 X.sup.- is a monovalent anion.
Sensitizing dyes of the aforementioned type are described in detail in German Pat. No. 2,608,082 (corresponding to U.S. Pat. No. 4,218,247).
German Pat. No. 1,904,629 (corresponding to U.S. Pat. No. 3,560,207) discloses an electrophotographic recording material containing an organic photoconductor in its photoconductive layer. The organic photoconductor is chemically activated and optically sensitized beyond the visible spectral region, by the addition of cyanine dyes which may contain substituents comprising, for example, unsubstituted or substituted thiazole, oxazole, selenazole, thiazoline, pyridine, quinoline, 3,3-dialkylindolenine, imidazole, imidazo(4,5-quinoxaline, 3,3-dialkyl-3H-pyrrolo(2,3-b)pyridine, or thiazolo(4,5-b)quinoline groups.
German Pat. No. 2,526,720 (corresponding to U.S. Pat. No. 4,063,948) discloses an electrophotographic recording material with an electrically conductive support, which is used to produce printing forms or printed circuits and is sensitized with cyanine dyes corresponding to the general formula ##STR2## wherein A is an unsubstituted or substituted indolyl group, an unsubstituted or substituted benzothiazolyl-amino group, an unsubstituted or substituted phenylamino group, or an unsubstituted or substituted indolinyl group, and
The sensitivity of the photoconductors is based, in principle, on the fact that the light energy which is available in the longer-wavelength region is absorbed by the sensitizing dyes and transferred to the photoconductor molecule.
Spectral sensitizations which result from the use of these sensitizing dyes often have the disadvantage, however, that they have a very wide sensitivity base. Recording materials prepared with the use of these dyes thus cannot be safely handled in the darkroom. This problem is particularly evident in the sensitizing dyes according to U.S. Pat. No. 4,334,001.
Use of these sensitizing dyes has the additional disadvantage that they sometimes possess several sensitization peaks and/or there is no pronounced sensitization peak at all. Frequently, the sensitization peak is not in the region of the strongest emission of the light source used for exposure, which is of critical importance, for example, in a recording material which is to be exposed to laser radiation. In addition, the spectral photosensitivity may often be increased, but the overall sensitivity is reduced or is not improved. These sensitizing dyes also often severely stain the photoconductive layer, which is inconvenient in some fields of application.